Support Byte Converters for mutable and immutable Maps, Sets, Seqs

[Lemmsjid]

Right now maps are serializable and deserializable if they're imported as the generic interface: scala.collection.Map[X,Y].

This is to support both mutable and immutable Maps, which are useful in different circumstances. However, in Scala you typically import immutable.Map, so it's confusing to require the generic interface.

Because mutable and immutable Maps are stored in the same binary layout, it's simple for Hpaste to support all interfaces simultaneously. So we'll do that.